The invention relates to a process and apparatus for adjusting the torque of an internal-combustion engine by regulating the ignition point and the air flow rate in an Otto engine, or by regulating the start and the duration of fuel injection in a diesel engine.
Modern Otto engines usually have an electronic throttle valve control system for regulating the air flow rate, in which the accelerator pedal is mechanically uncoupled from the throttle valve. To regulate the pertaining transmission line of a vehicle, modern engine--transmission management concepts use a torque interface in which the desired engine torque is normally adjusted either statically by means of a characteristic diagram which links the air flow rate, rotational engine speed and engine torque quantities, or dynamically by means of an air flow rate control. The dynamics of engine torque regulation by controlling only the air flow rate are significantly restricted by the finite speed of the throttle valve control element, and mainly by the filling characteristics of the suction pipe. However, certain engine functions, such as the idling regulating or traction upshift in the case of automatic transmissions, require a highly dynamic engine (that is, rapid) torque response, which cannot be satisfactorily achieved by the quasi-static air flow rate regulation. Conventionally, the required highly dynamic engine torque response is therefore achieved by ignition control, the resulting engine torque intervention not being coordinated with the air flow rate regulating. Such ignition control usually consists of a slight displacement of the ignition point, which is predetermined as a function of the engine operating point. In the case of diesel engines with electronic fuel injection, the demanded engine torque is conventionally adjusted exclusively by a corresponding selection of the injection duration, while the injection start is normally predetermined as a function of the engine operating point.
German Patent Document DE 42 15 107 C1 discloses a process for controlling an internal-combustion engine in which a desired value for the torque transmitted to the road is determined from the angular position of the accelerator pedal. Taking into account the transmitting function of the engine and of the transmission line, the fuel quantity to be injected into the internal-combustion engine is determined from this desired value. Based on the fuel quantity to be injected, a desired value is then determined for the required air flow rate taking into account a desired value for the fuel/air ratio, by inverting a predetermined suction pipe dynamics function. The air flow rate is then regulated by the corresponding adjustment of a throttle valve control element. The fuel quantity actually injected is then determined by means of the measured actual air flow rate.
German Published Patent Document DE 44 40 640 A1 discloses a process for transient control of an internal-combustion engine, which takes into account the accumulating effect of the suction pipe. For this purpose, a control unit uses an air flow rate density function (filed in a memory) to generate a value for the air flow rate at the cylinder input as a function of the suction pipe air density and the rotational engine speed. From this value a pertaining engine load value is then determined.
A fuel control unit for an internal-combustion engine disclosed in German Patent Document DE 41 12 908 A1 achieves a fast fuel control response during an engine acceleration without a reduction of the engine output torque, by following up the first injection calculated on the basis of the intake air temperature and of the internal cylinder pressure, with a second injection quantity which is calculated on the basis of the engine acceleration condition.
A device for controlling and/or regulating the fuel metering and/or the ignition angle of an internal-combustion engine disclosed in German Patent Document DE 39 42 966 A1 is designed so that, in the steady-state operation, the measuring value of a periodically fluctuating quantity (for example, the suction pipe pressure) which is crank-angle-synchronously measured once per ignition, is used always at the same crankshaft position for controlling or regulating the fuel metering or the ignition angle. In dynamic operation, on the other hand, every measuring value is used for controlling or regulating the fuel metering or the ignition angle. As a result, the transition from steady-state to dynamic engine operation can be recognized very rapidly, and can be taken into account in adjusting the fuel metering or the ignition angle.
German Patent Document DE 43 15 885 C1 discloses a process for adjusting the desired output torque of an internal-combustion engine, in which a desired engine load value is determined from the desired output torque, as a function of the rotational engine speed and the throttle valve opening angle. The measured actual value is regulated to the desired value by adjusting of the throttle valve control element. Conversion between regulation of the load and regulation of the air flow rate takes place by means of a load filter, which compensates the deviations of the measured air flow rate occurring in dynamic operating conditions from the air flow rate actually flowing into the combustion space. The transition between the two types of regulation can take place in a continuous or switched manner, preferably by using a one-sided hysteresis during the change-over from engine load regulation to air flow rate regulation.
One object of the present invention is to provide a process and apparatus of the initially mentioned type which adjusts the engine torque to a desired value with the least possible expenditures in both steady-state and transient engine operation with a comparatively short reaction time.
Another object of the invention is to ensure an engine operation with optimal fuel consumption and the exhaust gas emissions.
These and other objects and advantages are achieved by the torque adjustment process and apparatus according to the invention, in which the demanded desired engine torque is split into a dynamic component and a remaining quasi-static component. The dynamic component is used to determine corresponding adjustment of the ignition point in the case of an Otto engine or of the injection start in the case of a diesel engine. That is, the dynamic component is used as a command variable for a desired-engine-torque-dependent displacement of the ignition point or of the injection start, while the quasi-static desired torque component is regulated by means of a corresponding adjustment of the air flow rate (for an Otto engine) or of the injection duration (a diesel engine). In order to achieve minimal exhaust emission and fuel consumption, variation of the ignition point or of the injection start is expediently kept as small as possible. This means that the dynamic desired torque component represents exactly that part of the demanded desired engine torque which cannot be adjusted by the quasi-statically (that is, more sluggishly) reacting air flow rate or injection duration adjustment alone. Therefore, the present invention permits optimal coordination of quasi-static engine torque adjustment (by way of air flow rate and injection duration regulation) on the one hand, and highly dynamic engine torque adjustment (by regulating the ignition point or the injection start), on the other hand.
In a preferred embodiment of the invention, the dynamic desired torque component is determined by high-pass filtering of the demanded desired engine torque with a decay time constant which is selected as a function of the engine operating point.
In another preferred embodiment, a model-based estimation is made of the quasi-static desired torque component achieved by air flow rate or injection duration regulation. To obtain the dynamic desired torque component, the estimated value is subtracted from the demanded desired engine torque. In the simplest case, the model can be formed by a characteristic diagram of the quasi-static actual torque component as a function of rotational engine speed, engine cooling water temperature and, in the case of an Otto engine, the engine load and ignition point or, in the case of a diesel engine, the fuel quantity (and thus of the injection duration) and the injection start.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.